Merge pull request '"UNION with CTE" Workaround' (#65) from fix-union into master

Reviewed-on: #65
Reviewed-by: Lixfel <lixfel@steamwar.de>

src/de/steamwar/sql/internal/Statement.java

@@ -134,7 +134,11 @@ public class Statement implements AutoCloseable {
 
     public <T> T select(ResultSetUser<T> user, Object... objects) {
         return withConnection(st -> {
-            ResultSet rs = st.executeQuery();
+            boolean res = st.execute();
+            if(!res) {
+                throw new SecurityException("No result set for select statement");
+            }
+            ResultSet rs = st.getResultSet();
             T result = user.use(rs);
             rs.close();
             return result;